JP4900669B2 - Induction heating apparatus and electronic equipment - Google Patents

Description

  The present invention relates to an induction heating device used in electronic equipment such as an electrophotographic image forming apparatus, and more particularly to power control thereof.

Magnetic induction heating, in which a conductor is heated by an eddy current generated in the conductor by placing the conductor in a magnetic field, has been known for a long time and has been commercialized as an electromagnetic cooker. In recent years, there has been an apparatus that uses this technique as a heating device provided in a fixing unit of an electrophotographic image forming apparatus such as a copying machine.
In magnetic induction heating in such a heating device, an alternating magnetic field is generated by flowing a high-frequency current through a switching element in a resonance circuit realized using an exciting coil and a capacitor, and an eddy current is generated in the conductor by the change in the magnetic field. And heat. At that time, in order to keep the power supplied by the high-frequency current at an appropriate value, the power control is performed by measuring the input current using the current detection means. This current detecting means is also used for current monitoring for protecting the switching element. A large current flows through this switching element from the normal time, and if a current exceeding the rating flows due to an abnormality in the load, it will be destroyed in a short time, so current monitoring is necessary.

The prior art disclosed in Patent Document 1 is a fixing device using the above-described magnetic induction heating technology, and when heating a metal fixing belt, the maximum power is maintained at a constant value, and the output is reduced as the temperature rises. This makes it possible to realize faster and more stable on-demand fixing, as well as ensuring safety and enabling an emergency stop of the heating and fixing operation. Specifically, an excitation coil, a metal fixing belt that generates an eddy current by the excitation coil, a thermistor that detects temperature, and a current transformer that detects current flowing in the excitation coil, the current value detected by the current transformer Based on the control, the maximum value of the power supplied to the exciting coil is controlled, and the power supply to the exciting coil is stopped when the detected temperature of the pressure contact portion between the fixing belt and the pressure roller exceeds the specified temperature. Take control.
JP 2001-43964 A

  As described above, a large current flows through the switching element constituting the magnetic field generating means from the normal time, and when a current exceeding the rating flows due to a load abnormality, the switching element breaks down in a short time. However, in the related art including the fixing device disclosed in Patent Document 1, current detection is performed on a direct current from which ripples have been removed by rectification / smoothing processing. The switching element could not be protected against load fluctuations. The sudden load fluctuation means that the impedance suddenly decreases due to insulation failure (insulation breakdown due to leakage) of the exciting coil, or the load suddenly becomes open due to poor connector contact.

Moreover, in the prior art shown in Patent Document 1 in which an abnormality is detected by the temperature detection means, a time difference occurs because the distance between the heating unit and the temperature detection unit is physically separated, and a sudden load change or abnormality occurs. On the other hand, there is no effect of protecting the switching element.
The present invention is intended to solve such a problem of the prior art. Specifically, the magnetic sensor is used in place of the current detection means, and the response to the load abnormality is accelerated, and the switching is performed. It is an object of the present invention to provide a heating device that can prevent element destruction.

An induction heating apparatus according to the present invention includes an induction heating unit that causes an eddy current to be generated in a conductor placed in a magnetic field to overheat the conductor, and an induction heating control unit that controls the induction heating unit. In the heating device, detection means for detecting the strength of the magnetic field generated by the magnetic field generated by the excitation coil, two low-pass filters having different cutoff frequencies for removing high-frequency components from the detection signal output by the detection means, An abnormality detection means for detecting an abnormality based on an output of a first low-pass filter having a high cut-off frequency of the two low-pass filters, and a second low-pass filter having a low cut-off frequency of the two low-pass filters Power control means for controlling the power supplied to the exciting coil based on the output of

  According to the present invention, in the induction heating device that heats the conductor by generating an eddy current, the magnetic field strength of the magnetic field generated by the exciting coil can be detected by the detecting means. The amount of heating can be controlled. In addition, when the abnormality occurs, the abnormality detecting means having a fast response provided in the subsequent stage of the detecting means can quickly turn off the switching element for flowing the current that changes in the exciting coil, so that destruction of the switching element can be prevented.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the components, types, combinations, shapes, relative positions, and the like described in this embodiment are not merely intended to limit the scope of this description unless otherwise specified, but are merely illustrative examples. .
FIG. 1 is a schematic view showing the configuration of an electrophotographic copying machine incorporating a heating device as one embodiment of the present invention. This copying machine has, for example, a printer function and a facsimile function as functions other than the copying function. The copying function, the printer function, and the facsimile function can be switched and selected by an application switching key of the operation unit. The copy mode is selected when the copy function is selected, the print mode is selected when the printer function is selected, and the facsimile mode is selected when the facsimile function is selected.
Of these modes, the copy mode operates as follows.

When copying using an automatic document feeder (hereinafter referred to as ADF) 101, when the start key on the operation unit is pressed, the document at the bottom of the document stack placed on the document table 102 is fed. The paper is fed to a predetermined position on the document table (contact glass) 105 by the roller 103 and the feeding belt 104. The ADF 101 has a counting function for counting the number of documents every time one document is fed. The document on the document table 105 is discharged onto a sheet discharge table 108 by a feeding belt 104 and a discharge roller 107 after image information is read by an image reading device 106 serving as an image input unit.
When the next document is detected on the document table 102 by the document set detector 109, the lowermost document on the document table 102 is similarly placed on the document table 105 by the feed roller 103 and the feeding belt 104. It is fed to a predetermined position. The paper feed roller 103, the feed belt 104, and the discharge roller 107 are driven by a carry motor.

The first paper feeding device 110, the second paper feeding device 111, and the third paper feeding device 112 as the paper feeding means are respectively stacked on the first tray 113, the second tray 114, and the third tray 115 when selected. The transfer sheet is fed, and the transfer sheet is transported by the vertical transport unit 116 to a position where it contacts the photoconductor 117. The photoconductor 117 is a drum photoconductor and is driven to rotate by a main motor.
The image data read from the document by the image reading device 106 is converted into optical information by the writing unit 118 through an image processing means (not shown), and the charged surface on the photoconductor 117 is exposed with this optical information to form an electrostatic latent image. Is formed. The electrostatic latent image on the photoconductor 117 is developed by the developing device 119 to become a toner image.

  The conveyance belt 120 serves as a sheet conveyance unit and a transfer unit, and a transfer bias is applied from a power source. The transfer belt 120 conveys a toner image on the photoconductor 117 while conveying the transfer paper from the vertical conveyance unit 116 at a constant speed with the photoconductor 117. Transfer to transfer paper. The transfer paper is fixed with a toner image by a fixing device 121 and is discharged to a paper discharge tray 123 by a paper discharge unit 122. The photoreceptor 117 is cleaned by a cleaning device (not shown) after the toner image is transferred. The photoconductor 117, the charger, the writing unit 118, the developing device 119, and the transfer unit constitute a printer engine that forms an image on transfer paper.

The above operation is an operation for copying an image on one side of a sheet in the normal mode. However, when an image is copied on both sides of a transfer sheet in the duplex mode, the sheet feeding trays 113 to 115 are used. The transfer paper that has been fed and has an image formed on the front side as described above is conveyed by the paper discharge unit 122 to the double-sided input conveyance path 124 side, switched back by the reversing unit 125, and the front and back sides are reversed. It is transported to the transport unit 126.
The transfer paper transported to the double-sided transport unit 126 is transported to the vertical transport unit 116 by the double-sided transport unit 126, transported to a position where it abuts on the photoconductor 117 by the vertical transport unit 116, and on the photoconductor 117 as described above. The toner image formed on the back surface is transferred to the back surface and the toner image is fixed by the fixing device 121, whereby double-sided copying is performed. This double-sided copy is discharged to the paper discharge tray 123 by the paper discharge unit 122.
When the transfer paper is reversed and discharged, the transfer paper that is switched back by the reversing unit 125 and turned upside down is not conveyed to the duplex conveying unit 126 but discharged via the reverse discharge conveyance path 127. The paper is discharged to the paper discharge tray 123 by the unit 122.

  In the print mode, external image data is input to the writing unit 118 instead of the image data from the image reading device 106, and an image is formed on the transfer paper by the printer engine. In the facsimile mode, image data from the image reading device 106 is transmitted to the other party by a facsimile transmission / reception unit (not shown). Also, image data from the other party is received by the facsimile transmission / reception unit, and further input to the writing unit 118, and an image is formed on the transfer paper by the printer engine.

FIG. 2 is an explanatory diagram showing a schematic configuration of the fixing device 121. Hereinafter, the configuration of the fixing device 121 will be described with reference to FIG.
The fixing device 121 is configured as an induction heating type fixing device. In this configuration, the fixing roller 201 and the pressure roller 202 are provided so as to face the transfer paper conveyance path in the same manner as in a normal halogen heater system, and the fixing roller 201 is placed on the transfer paper on which the toner is transferred. The toner is heated and dissolved to be fixed on the transfer paper, and the pressure roller 202 applies pressure to the transfer paper to fix the toner. A heating roller 203 is provided at a position spaced from the fixing roller 201, and a fixing belt 204 is stretched between the heating roller 203 and the fixing roller 201. This fixing belt 204 is a member to be heated that is induction-heated by the exciting coil 8 and has a multi-layer structure including a heated metal portion (metal conductor), a non-thermally conductive portion and the like.

  The exciting coil 8 is for inductively heating the fixing belt 204 with an eddy current. In this embodiment, the exciting coil 8 has a structure in which a wire is wound in a spiral shape around a base body 206 that covers the outer peripheral surface of the heating roller 203 about a half circumference. . An electric current having an arbitrary frequency characteristic is applied to the exciting coil 8, and an eddy current flows through the heating roller 203 by receiving a magnetic flux generated by the electric current and is heated. The heat of the heating roller 203 is transmitted to the fixing belt 204 that rotates, and the heat and the nip pressure between the fixing roller 201 and the pressure roller 202 cause rotation between the fixing roller 201 and the pressure roller 202 in the rotational direction. The toner on the transferred transfer paper is fixed on the transfer paper.

  Further, the temperature of the fixing belt 204 is constantly monitored by a temperature sensor (thermistor) 19 close thereto, and if the temperature is lower than a predetermined control temperature (target temperature), the current supply (power supply) to the exciting coil 8 is continued. Stop supply. The temperature control is performed by a control circuit which will be described later, but a safety device that directly shuts off the power supply by the thermostat 208 is mounted when the temperature rises excessively. The fixing roller 201 is rotationally driven by a power source such as a motor, and the fixing belt 204 is moved and rotated by the power. The heating roller 203 is a driven roller that rotates by being suspended by the movement of the fixing belt 204.

  An encoder 209 that functions as a sensor for detecting that the fixing belt 204 is rotating is provided on the shaft of the heating roller 203. When the encoder 209 detects that the roller 203 is not rotating, it is determined that the belt has run out or slipped, and the current flowing through the exciting coil 8 is interrupted. Thereby, it is possible to prevent the fixing belt 204 from being locally heated for a long time and being burned out. That is, the fixing belt 204 does not rotate when the belt is cut or slipped, so that heat cannot be transferred, and the temperature of the fixing belt 204 that is stopped rises due to local continuous heating. Since the temperature sensor 19 for controlling the temperature is on the fixing roller side, the temperature does not rise unless the temperature is propagated by the fixing belt 204, so that the control side controls to increase the power more and more.

  As shown in FIG. 2, a magnetic sensor 20 for detecting the strength of the magnetic field generated by the exciting coil 8 is provided in the vicinity of the exciting coil 8. This will be described later. Further, the induction heating method is not limited to the illustrated external heating method, and may be, for example, an internal heating method in which an exciting coil is built in the fixing roller.

FIG. 3 is a block diagram showing the configuration of a conventional induction heating fixing control unit as an embodiment of the induction heating fixing control unit (corresponding to the induction heating control means described in the claims) in which the present invention is implemented.
In the induction heating and fixing control unit having the configuration shown in the figure, the current from the AC power source 1 is rectified by the rectifier circuit 4 to obtain a DC power source smoothed by a smoothing circuit constituted by the inductance 5 and the capacitor 6. Since the capacitor 6 is not a capacitor having a large capacity but is only capable of removing noise, the terminal voltage of the capacitor 6 remains a pulsating waveform that leaves the power supply period.
The current detector 2 is a current transformer, for example, and detects a current flowing through the induction heating fixing circuit. The voltage detector 3 detects a voltage input to the induction heating fixing circuit. As the voltage detector 3, a transformer is used to step down the power supply voltage.
The pulsating voltage across the capacitor 6 is switched at a high frequency by the switching element 9.

The resonance capacitor 7 and the excitation coil 8 (corresponding to the induction heating means described in the claims) are switched to cause a transient resonance, and the resonance current causes a magnetic field change in the excitation coil 8. An eddy current is generated in the heated body (heating roller 203) by electromagnetic induction due to the change in the magnetic field, and the heated body is heated by the heat generation of the resistance component caused by the eddy current flowing.
A temperature sensor 19 for measuring the temperature of the heated body is provided in the vicinity of the heated body. The temperature of the heated object measured by the temperature sensor 19 is input to the control circuit 48. Thereby, the control circuit 48 gives a control signal to the drive circuit 18 so that the temperature measured by the temperature sensor 19 becomes the target temperature, and the drive circuit 18 gives a high-frequency signal to the switching element 9.

  The current detection unit 2 always inputs the current value flowing through the entire circuit to the control circuit 48. As a result, the control circuit 48 determines that an abnormality has occurred when the input current is greater than or equal to the set value, shuts off the control signal sent to the drive circuit 18, and the drive circuit 18 provides the switching element 9. The switching element 9 is protected by stopping high-frequency signals and stopping oscillation. Similarly, the voltage detection unit 3 always inputs the voltage input to the induction heating fixing circuit to the control circuit 48. As a result, the control circuit 48 determines that the power supply is abnormal when the input voltage is equal to or higher than the set value, and cuts off the control signal sent to the drive circuit 18, and the drive circuit 18 provides the switching element 9. The switching element 9 is protected by stopping high-frequency signals and stopping oscillation.

Examples of the present invention will be described below.
[Example 1]
FIG. 4 is a block diagram showing the configuration of the induction heating fixing control unit and the like of the heating apparatus of this embodiment. In the induction heating and fixing control unit having the configuration shown in the figure, the rectifier circuit 4 rectifies the current from the AC power source 1, and the smoothing circuit constituted by the inductance 5 and the capacitor 6 smoothes the rectified voltage. Since the capacitor 6 is not a capacitor having a large capacity but is only capable of removing noise, the terminal voltage of the capacitor 6 remains a pulsating waveform that leaves the power supply period.
The voltage detection unit 3 is for measuring the voltage of the AC power supply 1, and uses a transformer to divide 100V to a low voltage and to insulate it from the primary side. The voltage divided by the transformer is rectified by a diode bridge, smoothed by a capacitor, converted to a direct current without voltage ripple, and becomes the illustrated input voltage (AN4) (this circuit is built in the voltage detector 3). ).

The switching element 9 switches the pulsating voltage across the capacitor 6 at a high frequency. As a result, the exciting coil 8 and the resonance capacitor 7 cause transient resonance, and the magnetic field is changed by the resonated current. An eddy current is generated in the heating roller 203 by electromagnetic induction due to the change of the magnetic field, and the heating roller 203 is heated by heat generation of a resistance component due to the eddy current flowing.
The magnetic sensor 20 detects the strength of the magnetic field generated by the exciting coil 8 and outputs a voltage. FIG. 5 shows that the magnetic sensor 20 outputs an output voltage (Vh) proportional to the magnetic flux density (B).

The output of the magnetic sensor 20 is input to the magnetic field detection circuit 21. The magnetic field detection circuit 21 has the following two roles.
(1) When the strength of the magnetic field detected by the magnetic sensor 20 is larger than the upper limit value or smaller than the lower limit value, a stop signal (STOP signal) is immediately sent to the drive circuit 18. As a result, the drive circuit 18 stops driving the switching element 9. Here, the switching element 9 and the drive circuit 18 constitute the power interrupting means described in the claims.
(2) The output of the magnetic sensor 20 proportional to the strength of the magnetic field (having a ripple voltage of the power supply frequency) is smoothed by a built-in low-pass filter (LPF), and the smoothed OUT signal (see FIG. 4) is supplied to the amplifier 44. give.

The power control means described in the claims will be described below. Details of the magnetic field detection circuit 21 will be described later.
First, the amplifier (magnetic field current converter) 44 converts the strength of the magnetic field of the exciting coil 8 into a corrected input current (AN3). The converted corrected input current corresponds to the strength of the magnetic field itself, and does not include power loss in the switching element 9 and the drive circuit 18 (that is, the current only for induction heating fixing).
The multiplier 14 multiplies the input voltage (AN4) and the corrected input current (AN3) and sets the result as corrected power. This is electric power consumed only by induction heating fixing, not including the loss of the switching element 9 and the power loss in the drive circuit 18.

This correction power is given to the differential amplifier 15 together with the target power obtained by the target power calculation circuit 13 by inputting the difference between the target temperature calculated by the differential amplifier 12 and the detected temperature from the temperature sensor 19, where Corrections are added to give the proper power. For example, when the correction power is high, power larger than the target power is input, so that correction is made to lower the correction power. When the correction power is low, power lower than the target power is input, so the correction power is increased. Add corrections. Then, the ON time calculation circuit 16 determines the PWM value from the corrected power value.
The ON timing generation circuit 11 generates a zero cross signal from the rectified AC signal. Then, the ON time generation circuit 17 uses this zero cross signal to generate a PWM signal to be supplied to the drive circuit 18 while preventing the switching element 9 from being suddenly turned on and destroyed at a high pulsating voltage. Drives the switching element 9.

FIG. 6 is a block diagram showing the configuration of the main part of the copier control system. In FIG. 6, the engine control unit 40 controls the induction heating fixing control unit shown in FIG. The switching element 9 heats the heating roller 203 by passing a current through the exciting coil 8. The temperature sensor 19 detects the temperature of the heating roller 03 and transmits it to the induction overheat fixing control unit and the engine control unit 40. In addition, the magnetic sensor 20 transmits the strength of the magnetic field to the induction overheating fixing control unit. The CPU 41 performs overall control.
FIG. 5 described above shows that the output voltage Vh of the magnetic sensor (for example, Hall element) 20 is proportional to the magnetic flux density B. That is, since the amount of heat generation is determined by the magnetic flux density (the strength of the magnetic field), the strength of the magnetic field detected by the magnetic sensor 20 represents the amount of heat generation of induction heating fixing itself.

FIG. 7 shows details of the magnetic field detection circuit 21. FIG. 8 shows signal waveforms and the like of the main part. Hereinafter, the operation of the magnetic field detection circuit 21 will be described with reference to FIGS. 7 and 8.
In this embodiment, a signal having a waveform as shown in FIG. 8A is output from the magnetic sensor 20, and a low-pass filter (LPF) 30 having a short delay time cuts high-frequency components and is shown in FIG. 8B. A signal having a waveform (LPF1 output) is output.
On the other hand, in the comparison voltage generation circuit 34 (corresponding to the reference voltage supply means described in the claims), the first comparator 31 and the second comparator 50 are supplied from the 50 Hz or 60 Hz AC divided voltage input from the voltage detector 3 (see FIG. 4). A comparison voltage to be supplied to the comparator 32 ( corresponding to a reference voltage described in claims ) is generated. The level of the power frequency signal from the voltage detection unit 3 is adjusted to generate a comparison voltage. A value for level adjustment can be freely set from the CPU 41. The first comparator 31 is supplied with a lower limit comparison voltage that is the lower limit value shown in FIG. 8 (3), and the second comparator 32 is supplied with the upper limit comparison voltage that is an upper limit value shown in FIG. 8 (5). As shown in FIG. 8, the power supply frequency components are left as they are in these comparison voltages. The comparators 31 and 32 correspond to the comparison means described in the claims.

  In the first comparator 31, when the LPF1 output shown in FIG. 8 (2) becomes lower than the lower limit comparison voltage, the first comparator output (UNDER signal) shown in FIG. 8 (4) is set to the high level. In FIG. 8, since the strength of the magnetic field suddenly decreases in section C, an abnormal signal (UNDER signal) is generated as a lower limit abnormality. For example, this is the case when a coil is partially shorted due to poor insulation. Further, in the second comparator 32, when the LPF1 output becomes higher than the upper limit comparison voltage, the second comparator output (OVER signal) shown in FIG. In FIG. 8, since the strength of the magnetic field suddenly increases in section B, an abnormal signal (OVER signal) is generated as an upper limit abnormality. For example, this is the case when the power supply voltage suddenly increases for some reason.

  The OR circuit 33 calculates the logical sum of the UNDER signal and the OVER signal, and generates a STOP signal when either abnormality occurs. The STOP signal is given to the drive circuit 18, and the drive circuit 18 stops driving the switching element 9. After this, the drive circuit 18 is configured so that it cannot be driven until the serviceman resolves the abnormality and cancels the abnormality even if the power is shut off and turned on again. Further, the UNDER signal and the OVER signal are input to the CPU 41 which is also the acquisition means described in the claims, and the CPU 41 determines which cause the abnormality has occurred, and displays the cause of the abnormality in a display device (display means in the claims). (Not shown). The operation flow on the CPU 41 side is shown in FIG. Hereinafter, this operation flow will be described.

This operation flow is executed when a STOP signal is output from the magnetic field detection circuit 21 during power control for the target temperature. At this time, as shown in FIG. 4, this STOP signal is given to the drive circuit 18, and the drive circuit 18 stops driving the switching element 9, but at the same time generates an interrupt to the CPU 41. As a result, the CPU 41 executes an interrupt process and takes in the UNDER signal and the OVER signal (step 1).
Subsequently, the CPU 41 determines the level of the two captured signals (step 2), and displays the determination result on the operation unit as a serviceman call (SC) (step 3). Whether UNDER or OVER has caused the stoppage is displayed. Further, the center is notified by communication means. In this way, the user can know the abnormality of heat fixing and the cause thereof, and can take an appropriate action.

Returning to FIG. Since the LPF1 output shown in FIG. 8 (2) includes a ripple voltage of the power supply frequency, the LPF1 output is smoothed to obtain the OUT signal (LPF2 output) shown in FIG. There is a need to. The second low-pass filter (LPF) 35 is for that purpose, and smoothes the ripple voltage by a circuit having a time constant sufficiently longer than the power supply frequency. This filter circuit comprises, for example, a resistor and a capacitor. If this time constant is not sufficiently large, even if it is not abnormal, the comparator 31 or the comparator 32 may detect it as abnormal. The dotted waveform shown in FIG. 8 (7) is the LPF1 output signal input to the LPF 35.
In this embodiment, the output of the LPF 35 having a large time constant is used as the OUT signal which is a feedback signal for exciting current control (excitation power control), whereas the detection of abnormal magnetic field strength is detected with a small time constant. The reason for this is to improve the response of abnormality detection. As a result, in this embodiment, it is possible to improve the response of abnormality detection as compared with the prior art while realizing highly accurate excitation current control.

FIG. 10 is an explanation comparing the detection current by the current detection means used in the prior art with the true detection current (detection current that does not include a loss in a switching element or the like) by the magnetic sensor 20 used in this embodiment. FIG. In FIG. 10, (a) is a conventional example including a loss (current detected by the current detection unit 2 shown in FIG. 2). This current is used for operating the control circuit even when induction heating fixing does not operate. Since it includes the idling current (shown as C in FIG. 10) and the loss of the switching element 9 during the induction heating fixing operation, it does not accurately represent the power that becomes heat in the induction heating fixing.
Further, (b) is a detection current that does not include a loss obtained from the strength of the magnetic field by the magnetic sensor 20, and more accurately represents the electric power that becomes heat in induction heating fixing. In FIG. 10, the hatched portion represents an error due to loss.

[Example 2]
FIG. 11 is a block diagram showing the configuration of an induction heating fixing control unit and the like of the heating apparatus of this embodiment. In this embodiment, the portion realized by the differential amplifier 12, the target power calculation circuit 13, the multiplication circuit 14, the differential amplification circuit 15, the ON time calculation 16, etc. in the configuration of the first embodiment shown in FIG. This is realized by the arithmetic processing unit 39 executed by the CPU 41. Hereinafter, a description will be given of parts different from the configuration of the first embodiment shown in FIG.
The basic operation of the arithmetic processing unit 39 is the same as that of the first embodiment.
In this embodiment, as shown in detail in FIG. 12, the integration type AD converter 36 is provided instead of the LPF 35 shown in FIG. 7, and the output of the magnetic field detection circuit 21 is used as the integration type AD converter. Digitized by 36 and passed to the CPU 41. Further, the output of the voltage detection unit 3 is digitized by the AD converter 45, and a digital voltage value (shown as DG4 in FIG. 11) is passed to the CPU 41.

FIG. 13 shows the timing of signals in the main part. Hereinafter, the operation of the magnetic field detection circuit 21a will be described with reference to FIGS. However, in FIG. 12, the operations of the comparator 31, the comparator 32, the OR circuit 33, and the comparison voltage generation circuit 34 are the same as those shown in FIG. The timing generation circuit 38 will be described.
First, the integration type AD converter 36 is a low-cost AD converter having a low conversion speed. As shown in FIG. 13 (2) as the integral ADC integration timing, the signal from the LPF 30 indicated as “LPF output” in FIG. 13 (1) is integrated in the integration interval, and AD is indicated at the timing indicated as “HOLD”. Holds the converted value. The held AD conversion value is updated when the next integration cycle ends.

The timing generation circuit 38 generates the “HOLD” signal as an integration timing signal of the integration type AD converter 36. Note that the divided voltage of the AC power supply of 50 Hz or 60 Hz is input to the timing generation circuit 38 via the voltage detector 3, and the integration timing signal is generated at the zero degree phase of the power supply voltage. As shown in FIG. 13 (3), the CPU 41 sets so as to integrate over several cycles of the power supply frequency.
As shown in FIG. 13 (4), the integration timing signal can be output every half cycle, for example, and the value after conversion by the integral ADC can be updated every half cycle as shown in FIG. 13 (5). In such a case, the AD conversion value is sensitive to changes in the magnetic field. When it is not necessary to react sensitively, the change in the magnetic field is integrated over several cycles and AD conversion is performed as in the integration ADC timing shown in FIG. In the latter case, as shown in FIG. 13 (3), the integral ADC output is less affected by fluctuations. In this embodiment, since a sudden magnetic field fluctuation is detected as an abnormality by the comparator 31 and the comparator 32, the integration type AD converter 36 has a longer integration time in order to increase the accuracy of power control.

Returning to FIG. 11, the operation of the magnetic field current conversion circuit 22 will be described.
The magnetic field current conversion circuit 22 is realized as a magnetic field current conversion table memory, and outputs data stored by addressing an input value from the magnetic field detection circuit 21. Note that the data stored can be freely rewritten by the CPU 41. The output of the magnetic field current conversion circuit 22 is a corrected input current (DG3), which is multiplied by the input voltage (DG4) by the CPU 41 to become corrected power.

FIG. 14 shows an operation flow of power control with respect to the target temperature executed by the CPU 41 in the arithmetic processing unit 39. Hereinafter, this operation flow will be described.
First, the CPU 41 sets a target temperature for induction heating and fixing in a memory (step 11). Then, the target power is calculated from the temperature difference between the target temperature and the temperature detected by the temperature sensor 19 (step 12). When the difference is large with respect to the target temperature, a large electric power is set, and when the difference is small, a small electric power is set.
Subsequently, the CPU 41 multiplies the digitized input voltage (DG4) by the correction input current (DG3) given by the magnetic field current conversion circuit 22 to obtain a correction power, and compares it with the target power. When the correction power is large (this is a case where the input voltage is high or the correction input current is large), the set power is corrected to be small, and conversely, when the correction power is small, the set power is corrected to be large ( Step 13). Further, the CPU 41 determines a PWM value (pulse width modulation value) from the corrected set power value and outputs it to the ON time generation circuit 17 (step 14).

Thereafter, the CPU 41 acquires the temperature measured by the temperature sensor 19 (step 15), and repeats from step 12 if the acquired temperature is lower than the target temperature (NO in step 16). On the other hand, if the target temperature has been reached (YES in step 16), the ON time of the ON time generation circuit 17 is set to 0, the power supply to the exciting coil 8 is stopped (step 17), and the operation flow is exited. .
The abnormality process shown in FIG. 9 is executed as an interrupt process during the execution of the operation flow from step 11 to step 17.
Thus, in this embodiment, the same effect as that of Embodiment 1 can be obtained.

1 is a schematic diagram showing the configuration of an electrophotographic copying machine as an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a schematic configuration of a fixing device provided in the copying machine as an embodiment of the present invention. It is a block diagram which shows the structure of the conventional induction heating fixing control part as one Embodiment of this invention. It is a block diagram which shows the structure of the induction heating fixing control part as 1st Example of this invention. It is explanatory drawing regarding the induction heating apparatus of the 1st Example of this invention. 1 is a block diagram showing a configuration of a main part of a copying machine control system as a first embodiment of the present invention. FIG. FIG. 3 is a block diagram illustrating a configuration of a main part of an induction heating fixing control unit as a first embodiment of the present invention. It is a figure which shows the signal waveform etc. of the principal part of an induction heating fixing control part as 1st Example of this invention. FIG. 3 is a flowchart showing an operation flow of a main part of the copier control system as the first embodiment of the present invention. It is another explanatory drawing regarding the induction heating apparatus of the 1st Example of this invention. It is a block diagram which shows the structure of the induction heating fixing control part as 2nd Example of this invention. It is a block diagram which shows the structure of the induction heating fixing control part principal part as 2nd Example of this invention. It is a figure which shows the signal timing etc. of the principal part of an induction heating fixing control part as 2nd Example of this invention. It is a flowchart which shows the operation | movement flow of the principal part of an induction heating fixing control part as 2nd Example of this invention.

Explanation of symbols

2 Current detection unit, 3 voltage detection unit, 7 resonance capacitor, 8 excitation coil, 9 switching element, 13 target power calculation circuit, 14 multiplier, 15 differential amplifier, 17 ON time generation circuit, 18 drive circuit, 19 temperature Sensor, 20 Magnetic sensor, 21 Magnetic field detection circuit, 22 Magnetic field current conversion circuit, 30 Low-pass filter, 31 First comparator, 32 Second comparator, 34 Comparison voltage generation circuit, 35 Low-pass filter, 36 Integral AD converter, 39 Operation Processing unit 41 CPU, 203 Heating roller

Claims (12)

In an induction heating apparatus comprising induction heating means for overheating the conductor by generating an eddy current in the conductor placed in a magnetic field, and induction heating control means for controlling the induction heating means,
Detection means for detecting the strength of the magnetic field generated by the magnetic field generated by the excitation coil;
Two low-pass filters having different cutoff frequencies for removing high-frequency components from the detection signal output by the detection means;
An abnormality detecting means for detecting an abnormality based on the output of the first low-pass filter having a high cutoff frequency among the two low-pass filters;
A power control means for controlling power supplied to the exciting coil based on an output of a second low-pass filter having a low cut-off frequency of the two low-pass filters;
An induction heating apparatus comprising: The induction superheater according to claim 1,
An induction heating apparatus characterized in that the detection means is a magnetic sensor. The induction heating apparatus according to claim 1 or 2,
Two comparison means are provided, and the output signal of the first low-pass filter having a higher cutoff frequency of the two low-pass filters is compared with the respective reference voltages by the two comparison means, and is higher than the higher reference voltage. Or a power cutoff unit configured to output an abnormal signal when the voltage is lower than the lower reference voltage, and to cut off power supplied to the exciting coil when the abnormal signal is output from any of the comparison units. An induction heating apparatus comprising: The induction heating device according to claim 3,
Induction heating device comprising an arrangement der Rukoto the current and the reference voltage is supplied to the exciting coil is a power supply frequency components. The induction heating apparatus according to claim 4 , wherein
An induction heating apparatus comprising reference voltage supply means for supplying two signals having different peak values obtained from an AC power supply side as two reference voltages to the two comparison means, respectively . In the induction heating apparatus according to any one of claims 1 to 5,
Induction heating apparatus that controls supply power to the exciting coil using a product of a current value generated based on a detection signal from the detection means and a voltage value generated based on an input voltage. . In the induction heating apparatus according to any one of claims 1 to 5 ,
An induction heating apparatus characterized in that a target power is obtained from a difference between a target temperature and a detected temperature, and supply power control to the exciting coil is performed based on the target power . An electronic apparatus comprising the induction heating equipment according to claim 1 or 2 wherein. An electronic apparatus comprising the induction heating device according to claim 3 . The electronic device according to claim 9, wherein
An electronic apparatus comprising: an acquisition unit configured to acquire whether the interruption of the supplied power by the power interruption unit is caused by an excessive or small magnetic field strength . The electronic device according to claim 10 , wherein
Electronic equipment comprising display means for displaying information taken in by the acquisition means . The electronic device according to claim 10 , wherein
An electronic apparatus comprising a communication unit that notifies an external device of information captured by the acquisition unit .

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